A by-wire type device in which a driver-requested driving or braking force is detected by the pressed amount of a stroke sensor mounted on a foot pedal, then an actuator is controlled to provide a driving or braking force corresponding to the detected driver-requested acceleration has been proposed, for example, in JP-A-06-206531 (PTL 1). Note that the detail of the control is described later.
By the way, a typical foot pedal of currently mass-produced vehicles has a length from the pedal pressing position to the fulcrum of several tens of centimeters and a maximum pedal pressed amount of several centimeters or so. Consequently, the stroke amount from the pedal releasing position to the maximum pressed position (hereinafter referred to as a full stroke) converted in angle has been proved to be only a few degrees through an experiment performed by the inventors. In order to accurately control the driving or braking force according to the driver's request, the very small change in the angle described above needs to be accurately detected, which requires a higher-precision sensor, causing a problem of increasing the size and cost of the sensor.
Now, the operation of a foot pedal and an actuator that are not by-wire type is described. Supposing that the foot pedal is a brake pedal and the actuator is a brake, the braking force to be applied is expected to be proportional to the pressed amount of the foot pedal pressed by the driver. Similarly, when the foot pedal is an accelerator pedal and the actuator is an engine output, the driving force is expected to be proportional to the pressed amount. This operation should be consistent, independent of whether the above-described by-wire type system is employed or not. If this operation is inconsistent, the driver feels uncomfortable, which causes the commercial value of the vehicle to be reduced.
So, in order to provide a by-wire type system with a low-cost configuration, the inventors experimented a system in which a low-precision angle sensor is used as a brake stroke sensor to apply braking to a vehicle according to the detected driver-requested braking force. As result, a problem occurred in which the system responds sensitively to a small braking operation due to its coarse detection precision, so the system recognizes the amount of change in the driver-requested braking force more sensitively than the driver recognizes, which causes the driver to feel uncomfortable.
In other words, even when the driver-requested braking force detected by a stroke sensor changes rapidly, if the amount of change is small, that rapid change is due to low detection precision of the brake stroke sensor, so the system is expected to determine that the driver has requested a slow increase in the braking force rather than a rapid braking; and if the amount of change is large, the system is expected to determine that the driver has requested a rapid braking and to rapidly increase the braking force. However, the problem was that this operation cannot be achieved with the low-precision brake stroke sensor.
This problem occurs when the low-precision angle sensor is used to control the actuator in order to provide a by-wire type system with a low-cost configuration. Needless to say, this problem applies to not only the brake pedal, but also the accelerator pedal.
Here, the PTL 1 discloses a technique including a function in which if determined that the operation speed per unit time of a brake pedal is higher than or equal to a predetermined value, it is determined that a rapid braking is requested, then the relationship between the amount of operation detected by an operation amount detection means and the amount of actuation control of an actuator is changed based on the determination result.